Method of creating numerical control data for rough machining

ABSTRACT

This invention relates to a method of creating NC data for rough machining, in which a cutting path (QLi) for rough machining is outputted using points on an i-th point sequence path (PLi) from among a plurality of point sequence paths repeatedly digitized at a predetermined interval in a predetermined direction. The next cutting path for rough machining is created and output using a projected point sequence path (PLk&#39;) which, among those projected point sequence paths spaced away from the i-th point sequence path by a distance greater than a tool radius (Tr), is that nearest an i-th projected point sequence path (PLi&#39;).

TECHNICAL FIELD

This invention relates to a method of creating Numerical Control (NC)data for rough machining. More particularly, the invention relates to amethod of creating NC data for rough machining in which a workpiece isroughed out by a tool of a predetermined radius using surface data (toolnose position data) digitized by tracing or the like.

BACKGROUND ART

There is a method of creating NC data for machining in accordance withthe profile of a model using model surface data digitized while tracingis executed.

FIG. 4 is an explanatory view in which surface data of a model MDL aredigitized by X-Z two-way surface tracing. This involves moving a stylusSTL along the X axis at a predetermined tracing velocity, allowing thestylus to move up and down along the model MDL in the direction of the Zaxis, and storing three-dimensional position data indicative of stylusposition every predetermined time. When the boundary of a tracing regionTRR is reached, a predetermined amount of pick-feed is performed in thedirection of the Y axis, after which surface tracing is similarlyexecuted in an opposite x-axis direction. During this surface tracing,the position of the stylus STL is monitored, the resulting position dataare accepted and the surface of the model MDL is digitized. The surfacedata are subsequently employed to create NC data.

For cases in which a workpiece is subjected to roughing-out machining bya tool 21 of a predetermined diameter using a plurality of digitizedpoint sequence path data a in the prior art, a method has already beenput into practical use in which NC data for rough machining are createdwhile skipping a number of point sequence paths at equal intervals. Forexample, letting Ll ˜L7 represent a plurality of digitized pointsequence paths, as shown in FIG. 5, Ll, L4 and L7 are adopted as thecutting paths for rough machining, with two point sequence paths (L2, L3or L5, L6) being skipped between each adopted path.

After rough machining tool 21 performs machining from right to leftalong, the point sequence path Ll, a pick-feed is performed in theY-axis direction and then machining is carried out from left to rightalong the next point sequence path L4. This means that the regionactually machined by the rough machining tool 21 by movement along thelatter L4 path is solely the portion (the shaded portion) indicated byA, with the remaining portion being a region already cut, namely anon-cutting region E overlapping the previously cut path.

Accordingly, if the number of skipped point sequence paths is designatedimproperly, the non-cutting region E will be larger than the actuallycut region A. In other words, the overlap of the previously cut pathconsumes too much time and efficiency suffers.

An object of the present invention is to provide a method of creating NCdata for rough machining in which, when a workpiece is subjected toroughing-out machining by a tool of a predetermined radius using aplurality of digitized point sequence path data, non-cutting regions arereduced so that highly efficient roughing-out machining can beperformed.

DISCLOSURE OF THE INVENTION

In a method of creating NC data for rough machining according to thepresent invention, a first cutting path for rough machining is outputtedusing an i-th point sequence path PLi from among a plurality of pointsequence paths repeatedly digitized at a predetermined interval in apredetermined direction. A second cutting path for rough machining isthen generated and as a point sequence path which among the pointsequence paths spaced away from the i-th point sequence path PLi by adistance greater than the tool radius, is the point sequence pathnearest the i-th point sequence path PLi (first cutting path).

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 (a) and 1 (b) views are for describing the general features ofthe method of the present invention;

FIG. 2 is a block diagram of an apparatus (a digitizer) for practicingthe method of the invention;

FIG. 3 is a flowchart illustrating processing for creating roughmachining NC data according to the method of the invention; and

FIGS. 4 and 5 are explanatory views of an example of the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1 (a) and 1 (b) are views for describing the general features ofthe method of the present invention, in which FIG. 1 (a) is a view inwhich point sequences digitized by X-Z surface tracing are projectedonto an X-Y plane, and FIG. 1 (b) is a sectional view taken along ani-th point sequence path PLi.

Numeral 21 denotes a tool for rough machining, Tr the radius of theroughing tool 21, PLi an i-th point sequence path, PLi' a point sequencepath obtained by projecting this point sequence path onto the XY plane,QLi a cutting path for rough machining corresponding to the pointsequence path PLi, P(i,j) a j-th digitized point on the point sequencepath PLi, R(i,j) a point obtained by projecting the digitized pointP(i,j) onto the X-Y plane, and Q(i,j) a point on the rough machiningcutting path QLi corresponding to the digitized point P(i,j).

When the cutting path QLi for rough machining is outputted using thei-th point sequence path PLi, the next cutting path for rough machiningis created and outputted using a projected point sequence path PLk'which, among those projected point sequence paths spaced away from aprojected point sequence path PLi' in the XY plane by a distance greaterthan the tool radius Tr, is that nearest the projected point sequencepath PLi'.

FIG. 2 is a block diagram showing an apparatus (a digitizer) forpracticing the method of the present invention.

In FIG. 2, numeral 1 denotes a digitizer equipped with an NC datacreating function in addition to a digitizing function for accepting thepresent position of a tracer head while tracer control is being effectedThe digitizer 1 has a processor 1a, a ROM 1b for storing a controlprogram, a RAM 1c for storing digitizing data, and a working memory 1d.

Numeral 2 denotes an operator's panel having functions for inputtingvarious operation signals and setting tracing conditions, the tracingregion TRR (see FIG. 1), the tracing method, a feedback amount Δp andthe tool radius Tr, etc.

Numerals 10X, 10Y, 10Z denote DA converters for converting velocity data(digital values) along respective axes commanded by the digitizer 1 intorespective analog velocity signals V_(x), V_(y), V_(z). Numerals llX,llY, llZ denote X-, Y- and Z-axis servo circuits, respectively, 12X,12Y, 12Z denote X-, Y- and Z-axis servomotors, respectively numerals13X, 13Y, 13Z represent pulse generators for generating single pulsesX_(f), Y_(f), Z_(f), respectively, each time the corresponding motorsrotate through a predetermined angle. Numeral 14 denotes a presentposition register for reversibly counting the pulses X_(f), Y_(f),Z_(f), in accordance with the direction of movement, to store thepresent positions along the respective axes. Further, TH represents atracer head, STL a stylus, and MDL a model.

FIG. 3 is a flowchart illustrating a process for creating roughmachining NC data according to the method of the invention. Processingfor creating rough machining NC data according to the invention will nowbe described in accordance with the flowchart of FIG. 3. It will beassumed here that the coordinates of a number of points [referred to as"digitized points" and indicated by the positions of the black circlesin FIG. 1(b)] on the model surface MDL have already been accepted by adigitizing processor such as digitizer 1 based on X-Z surface tracing,and that these coordinates have been stored in the RAM 1c.

First, the processor la performs the operations 1 →i, 1 →j (step 101).

Next, it is determined whether position data indicative of the j-thdigitized point P(i,j) on the i-th point sequence path PLi is present inthe RAM 1c (step 102). In the absence of the data, the processing fromstep 105 onward is executed. If the data are present in memory, theprocessor obtains the point R(i,j), which is the projection of thedigitized point P(i,j) onto the XY reference plane, and erases from theRAM 1call position data indicative of digitized points corresponding toprojected points contained in a circle Ci whose center is the pointR(i,j) and whose radius is the tool radius Tr (step 103).

Thereafter, the rough machining point Q(i,j) [e.g., a point, apredetermined value Zi above the digitized point P(i,j)] correspondingto the digitized point P(i,j) is outputted (step 104).

Next, the processor la determines whether j =n(i) holds, where n(i) isthe number of digitizing points on the i-th point sequence path PLi(step 105). If j <n(i) is found to hold, then the operation

    j +1 →j

is performed (step 106) and processing is repeated from step 102 onward.

If j =n(i) is found to hold, on the other hand, it is determined, bychecking to see if i =m holds, whether processing has been terminated atthe m-th point sequence path, which is boundary of the tracing regionTRR (step 107). If processing has not been terminated at the m-th pointsequence path defining the boundary of the tracing region TRR, theoperations

    i +1 →i

    1 →j

are performed (step 108) and processing is repeated from step 102onward.

Processing is ended if processing has been terminated at the m-th pointsequence path defining the boundary of the tracing region TRR.

Thereafter, NC data for rough machining are created based on pointsequence data of the rough machining point Q(i,j) outputted at step 104.

Thus, in accordance with the present invention, when creating NC datafor roughing out a workpiece by a tool of a predetermined radius using aplurality of digitized point sequence pass data, point sequence pathsused in creating the NC data for rough machining are selectedautomatically based on the tool radius. As a result, there are but a fewnon-cutting regions so that NC data can be created for highly efficientrough machining.

We claim:
 1. A method of creating numerical control data for roughmachining in which a workpiece is subjected to roughing-out by a tool ofa predetermined radius, said method using point sequence paths selectedfrom among a plurality of point sequence paths previously produced bydigitizing a surface of the workpiece repeatedly at a predeterminedinterval in a predetermined direction, said method comprising the stepsof:(a) outputting a first cutting path for rough machining on thesurface of the workpiece along an i-th point sequence path PLi; (b)projecting each point sequence path onto a plane to produce projectedpoint sequence paths; (c) obtaining an i-th projected point sequencepath PLi' representing said i-th point sequence path PLi projected ontothe plane; (d) obtaining in the plane a k-th projected point sequencepath PLk' which among the projected point sequence paths spaced awayfrom said i-th projected point sequence path PLi' by a distance greaterthan said predetermined radius of the tool is nearest said i-thprojected point sequence path PLi'; and (e) generating and outputting asecond cutting path on the surface of the workpiece for rough machiningby selecting a k-th point sequence path among the point sequence paths,corresponding to said projected point sequence path PLk'.
 2. A method ofcreating numerical control data for rough machining according to claim1, characterized by adopting a point Q(i,j), which is located above apredetermined point P(i,j), on said point sequence path PLi by adistance of a predetermined value, as a point on the cutting path forrough machining.
 3. A method of creating numerical control data forrough machining according to claim 1, characterized by:projecting eachpoint sequence path onto a predetermined plane; obtaining a circle whoseradius is the tool radius and whose center is a projected point R(i,j)obtained by projecting a point P(i,j) on said point sequence path PLionto the predetermined plane; eliminating all projected points containedwithin said circle as points not related to cutting paths for roughmachining; and outputting a cutting path for rough machining usingpoints on a cutting path that correspond to the remaining projectedpoints.
 4. A method of machining a workpiece using a tool of apredetermined radius, said method comprising the steps of:(a) machiningalong a first cutting path, said first cutting path being a first pointsequence path of a plurality of point sequence paths representing theworkpiece; (b) selecting a second cutting path from among the pluralityof point sequence paths representing the workpiece, said second cuttingpath being selected from among the point sequence paths as (i) closestto said first cutting path and (ii) further than the predeterminedradius from said first cutting path; and (c) machining along the secondcutting path.
 5. A method of machining a workpiece using a rotary toolhaving a radius defining a circular cut region, the workpiece beingmapped according to a plurality of parallel lines, each line consistingof a plurality of points, said method comprising the steps of:(a)identifying mapping information for a particular point on a particularline; (b) checking if the mapping information indicates machining hasnot occurred for the particular point on the particular line; (c)recording mapping information that indicates machining has occurred forall points on all lines within the radius of the rotary tool centered atthe particular point on the particular line if the checking indicatesmachining has not occurred for the particular point on the particularline; (d) generating numerical control commands to move the rotary toolto be centered at the particular point on the particular line if thechecking indicates machining has not occurred for the particular pointon the particular line; (e) repeating steps (a) through (d) for all ofthe plurality of points on the particular line; and (f) repeating steps(a) through (e) for all of the plurality of lines.